Orange Outline/Selection Problem
Yellow/orange outline just means that the object(s) are selected. So, do you mean you just want to DESELECT the object(s)? If yes, then you can go to menu Select > (De)select All or shortcut A (toggle Select/Deselect All).

BTW, why do you learn version 2.79? The keymap is using RIGHT click for selecting object, and doesn't go away with left click on empty space. This will confuse you if you are not familiar with it. And the problem that you asked this is you skipped the basic of Navigation in Blender. So I recommend you to use version 2.8x with the LEFT click for selection, and it's more intuitive for new users coming from other programs.

This is manual for selection in 2.8x : Selecting Manual